Fitted scale versus source units
Fitted scale makes a model conveniently visible within the detected scene. It is useful for shape discussion but does not represent real-world dimensions.
Source-unit placement uses your chosen interpretation of the model coordinates. That can be closer to intended size, but STL does not declare units and tracking is not metrology-grade.
What affects AR accuracy
Lighting, surface texture, device motion, scene size and tracking quality all influence placement stability. A model can drift or appear slightly offset as the device refines its understanding of the room.
Use AR to communicate and explore. Verify installation clearances, safety distances and fabrication dimensions with approved measurements and engineering documents.
Prepare a model for mobile AR
Very dense meshes can be slower to load and manipulate. A simplified review export often provides a smoother field experience while preserving the shape needed for discussion.
Remove confidential or unnecessary components before sharing a model with another person, even when the viewer itself operates locally.